Leon:
-His attack upgrade which grants him 15% critical strike chance for 36 damage just needs to go down... Either percentage or the flat damage. Or both.
-Being able to stay invisible forever needs tweaking. It would make much more sense if it lasted around 5-10 seconds, still being useful for quick ambushes and escapes.

Yuri:
-Many ways to exploit all of the maps.
-Drop mines everywhere from above, lock the top lane. Mine damage is too high; either total number of mines allowed at a time needs to be limited, or their damage needs to go down.
-Flying all the time; if the player wishes, you won't be able to touch him while he's hovering around, dropping mines, and locking the top lane for good. Not only that; with his reflecting laser, he can hover in places where he can shoot at the tower freely. Or drop mines (not bouncy ones) near tower non stop, eventually destroying the tower aswell.
-On top of all this, he can get a slowing&healing aura. With all the benefits & exploits that flying&mines&reflecting laser grants him, he also gets a slowing&healing aura...

Lonestar:
-Not exactly an exploit, but on one of the maps, jump-pads (or whatever you call them) needs to be changed. Because, if you get knocked back by a bull, you'll hit the jump-pad and get away from the action unintentionally.

These are the issues I see with the game. Aside from that, nice change of scenery. I just wish there was a bit more skills for each of the characters; instead of attack-skill1-skill2, I wish there was attack1-attack2-skill1-skill2-skill3-skill4, and you pick one attack with two skills. Diversity is always nice in these games.

Yuri however is very much counterable(at least in my experience.). In maps where there was a high ceiling, I was able to easily bring him down as Froggy G. Any stun I believe will also take him down as well. Also he needs to rely on the flight adv. if he ANY chance to survive. due to the laser being weak as hell on 1v1 fights and being pretty slow when the going gets tough, he kinda needs the mines and jetpack.